JP4781813B2 - Manufacturing method of molten iron - Google Patents

Description

  The present invention relates to a method for producing molten iron by preliminarily reducing powder containing iron oxide to reduced iron and supplying the reduced iron together with carbonaceous material and oxygen to a melting furnace in which seed water is present.

  As a converter steelmaking method using solid iron-containing cold materials such as granule, mold and scrap generated from steelworks, conventionally iron-containing cold materials, carbonaceous materials, and oxygen are supplied to a melting-only converter where seed water is present. The required amount is obtained by obtaining the total amount of high-carbon molten iron of the required amount of seed water in the converter dedicated to melting and the required amount of refining in another converter dedicated to refining, and oxygen refining in the converter dedicated to refining using this high-carbon molten iron as a raw material The converter steelmaking method to obtain the molten steel of the component is known, and if the sulfur content of the carbon material used in the melting dedicated converter is high and the sulfur content of the high carbon molten iron is high, It is also known to desulfurize with a ladle before oxygen refining (Patent Document 1).

  In such a steelmaking method consisting of a melting-only converter and a refining-only converter using the entire iron-containing cold material as a raw material, the generation of dust containing iron as a main component cannot be completely eliminated in the melting-only converter and the refining-only converter. Therefore, it is necessary to efficiently recycle dust mainly composed of iron generated in a melting-dedicated converter and a refining-dedicated converter to solve the dust processing problem and improve the iron yield.

  In Patent Document 2, dust generated in a melting-dedicated converter and a refining-dedicated converter and lime content up to 15% or carbon material up to 35% are combined to form a lump by dish-type granulation method, compression molding method, etc. In order to prevent dissipation outside the converter due to the rising gas flow due to gas generation inside the converter when it is charged and reused by natural fall from the upper part of the converter, the particle size of 10 mm or more in the melting-only converter, In a refining converter, a method of reusing agglomerated dust having a particle size of 5 mm or more has been proposed. According to this method, the problem of processing the generated dust can be solved, and the generated dust can be efficiently recovered as iron, which is beneficial.

  Dust generated in a melting-only converter or a refining-only converter supplies pure oxygen, for example, by performing top blowing, so that most of iron is oxidized. In order to reduce and melt iron oxide, for example, ferrous oxide, a heat amount about four times that of pure iron is theoretically required. Therefore, when the agglomerated dust containing iron oxide is recycled to, for example, a melting-only converter, the amount of heat necessary for producing the molten iron is increased as compared with the case where the agglomerated dust is not recycled.

  On the other hand, the upper limit of the furnace heat supply rate (oxygen supply rate, carbon material supply rate) of the melting-dedicated converter is fixed by the oxygen supply facility capability, the carbon material supply facility capability, and the dust collection exhaust gas treatment facility capability. There is a problem that the production rate of molten iron decreases due to an increase in the amount of heat necessary to produce molten iron. In addition, since the heat of combustion of pure oxygen and a carbonaceous material, such as coal, is used as a heat source necessary for the above-described reduction, oxygen and the carbonaceous basic unit increase by that amount, and the manufactured molten iron by S in the carbonaceous material, for example, coal. An increase in medium [S] is a problem.

  In Patent Document 3, as shown in the flow in FIG. 7, carbonaceous materials are agglomerated and agglomerated in dust generated in the melting converter 1 and the refining converter 3, and heated at a high temperature in the preliminary reduction furnace 8. A dust utilization method is disclosed in which after the internal carbonaceous material is preliminarily reduced as a reducing material, it is supplied to the melting-only converter 1 where seed hot water is present as a part of the iron-containing cold material at a high temperature and reused. As a result, after the agglomerated dust is preliminarily reduced and supplied to the melting-dedicated converter in a high temperature state, the supply amount of oxygen and carbon as a reduction heat source to the melting-dedicated converter 1 is reduced. Since a unit is reduced, the fall of the productivity of molten iron can be suppressed and the increase in [S] in manufactured molten iron can be suppressed.

In the method of burning the carbon content in the furnace with oxygen while supplying the carbonaceous material as described above and melting the iron-containing cold material by the heat of combustion, the carbon content is burned as close to complete combustion as possible, Obtaining combustion heat and efficiently transferring the heat to the iron-containing cold material is the key to efficiently dissolving the iron-containing cold material with a small amount of carbon and oxygen consumption. That is, it is important to set the secondary combustion rate and the heat receiving efficiency defined by the following equations as high as possible.
Secondary combustion rate = [(CO ₂ ) + (H ₂ O)] / [(CO ₂ ) + (CO) + (H ₂ O) + (H ₂ )] × 100 (3)
Heat receiving efficiency = [1- (exhaust gas super heat) / (secondary combustion heat generation)] × 100 (4)
However, (CO ₂ ), (CO), (H ₂ O), and (H ₂ ) all represent the concentration (volume%) of each component in the exhaust gas. Further, the exhaust gas superheat represents a portion of the exhaust gas sensible heat that is equal to or higher than the metal temperature, and the secondary combustion heat generation represents the heat generation amount due to CO + 1 / 2O ₂ → CO ₂ .

In Patent Document 4, an upper bottom blown converter type vessel is used, the amount of slag in the furnace is 100 to 1000 kg per 1 ton of molten iron in the furnace, and the slag recess depth L _S and the oxygen jet by the top blown oxygen jet are while吹酸as hit have a ratio L _S / L _S0 of the slag thickness L _S0 parts not is within the range of 0.5 to 1, 5 to 200% more of carbonaceous material amount in the slag of the slag amount It is said that both the secondary combustion rate and the heat receiving efficiency can be maintained at a high value.

  Basic refractories are used as the lining refractories of converters, and recently MgO-C bricks are used in particular. In order to extend the refractory life by suppressing the melting rate of such MgO-based refractories, a technique is known in which dolomite or the like is added to the slag to keep the MgO concentration in the slag close to the saturation concentration ( For example, Non-Patent Document 1).

Japanese Examined Patent Publication No. 4-11603 Japanese Patent Publication No. 4-38813 JP 2000-45012 A Japanese Patent Laid-Open No. 8-325621 Third Edition Steel Handbook II Steelmaking and Steelmaking Pages 487-488

  In the method described in Patent Document 3, the metallization rate of the prereduced dust is not 100%. Patent Document 3 describes that the metallization rate can be increased by raising the reduction temperature. However, raising the reduction temperature reduces the productivity of the prereduction furnace or the energy intensity required for the prereduction. cause. In order to ensure the productivity of the preliminary reduction furnace, the metallization rate is preferably about 80 to 85%, although it depends on the raw material dust component. Then, even if it is said that it is metalized to 80-85%, when supplying reduced iron with iron-containing cold materials, such as scrap, to a melting exclusive converter, the remaining 15-20 which is not metallized It is necessary to supply excess oxygen and carbonaceous material in order to metalize the% component and secure the necessary heat, which causes a reduction in the production rate of molten iron.

  In this way, in melting reduced iron having a metallization rate of about 80 to 85%, a melting furnace for melting reduced iron is provided separately from a melting furnace for melting iron-containing cold materials such as scrap. This is preferable because high productivity can be secured as a whole. The unreduced iron oxide is reduced by a reaction with the carbonaceous material supplied in the hot metal, and the amount of heat required for the reduction is compensated by the combustion heat of the supplied carbonaceous material and oxygen.

  Therefore, pre-reduced reduced iron was used as iron-containing cold material, charged into a melting furnace where seed hot water was present, and dissolved by supplying carbonaceous material and oxygen, and then melted using scrap as iron-containing cold material. As compared with the case, it was found that the heat receiving efficiency represented by the formula (4) is lowered. If the heat absorption efficiency is low, the oxygen intensity and carbon material intensity required to dissolve the reduced iron will increase, and the productivity will deteriorate, and the low heat efficiency will mean that the exhaust gas temperature will rise. It means increasing the refractory load.

  The present invention provides a method for improving the heat receiving efficiency while maintaining the secondary combustion rate at a high level in a molten iron production method for obtaining molten iron by supplying reduced iron together with carbonaceous material and oxygen to a melting furnace in which seed hot water exists. This is the first purpose.

As a method for supplying the carbonaceous material to the melting furnace, a method of blowing pulverized coal together with a carrier gas from the bottom of the converter furnace and a method of adding massive coal from above are used in combination. However, a part of the added carbonaceous material is not dissolved in the hot metal, but is scattered in the furnace space. If the scattered carbon powder is present, a solution loss reaction (C + CO ₂ → 2CO) occurs in the furnace, and the secondary combustion rate cannot be sufficiently increased.

  The second object of the present invention is to provide a method for increasing the high secondary combustion rate without causing the solution loss by causing the carbonaceous material added to the furnace to be efficiently dissolved in the hot metal and scattered in the furnace space. Objective.

  The first invention will be described.

  MgO-C refractory is used as the refractory lining for the melting furnace. In order to prevent melting of the refractory, light burned dolomite or light burned magnesite is introduced into the slag in the melting furnace. The MgO concentration of the slag is increased to a value near the saturation concentration (12 to 18% by mass).

When preliminary reduction is performed using dust generated from a melting-only converter and a refining-only converter using iron-containing cold material as a raw material to produce reduced iron, the concentration of Al ₂ O ₃ in the reduced iron becomes high. When the reduced iron produced in this way is used as an iron-containing cold material and melted in a melting furnace, the Al ₂ O ₃ in the reduced iron is dissolved in the slag, and the Al ₂ O ₃ contained in the carbon material is also converted into the slag. since dissolved, Al ₂ O ₃ component of the slag is 12 to 18 wt% and a high value.

As described above, in the slag in which both the MgO concentration and the Al ₂ O ₃ concentration in the slag show high values, the slag composition control adopted in the conventional melting method for melting the iron-containing cold material is sufficient for the slag to hatch. The slag fluidity cannot be sufficiently obtained.

Even if the secondary combustion rate in the furnace space is maintained at a high level and heat is obtained, if the slag fluidity is poor, the heat from the furnace space to the hot metal through the slag is not sufficiently performed, It was found that the heat receiving efficiency was lowered. It has been found that the reason why the heat receiving efficiency decreases when reduced iron is used as the iron-containing cold material is that the fluidity of the slag deteriorates due to the slag component. Then, the slag showing a both high value MgO concentration and the concentration of Al ₂ O ₃ in the slag, and to clarify the relationship between the slag component and temperature in order to ensure the fluidity of the slag.

The present invention has been made on the basis of the above knowledge, and agglomerated by agglomerating a carbonaceous material in a powder containing iron oxide, preliminarily reduced by heating at a high temperature in a prereduction furnace and using the interior carbonaceous material as a reducing material. Then, the produced reduced iron is supplied to a melting furnace in which seed water is present together with carbonaceous material and oxygen, and the slag composition produced on the molten iron is in mass%, Al ₂ O ₃ : 12 to 18%, MgO: 12 The molten iron production method is characterized in that the A in the following formula (1) relating to the basicity B of the slag to be produced and the molten iron temperature T (K) after dissolution is less than 5:
A = 7 * 10 < ^-7 > * exp (-6.2143 * B) * exp ((20663 * B + 7655.1) / T) (1)
B = CaO (mass%) / SiO ₂ (mass%)

By setting A in the above formula (1) to less than 5, sufficiently high slag fluidity can be ensured despite the high concentrations of Al ₂ O ₃ and MgO in the slag, and as a result, the heat receiving efficiency can be improved. As a high value, the carbonaceous material and oxygen intensity required for dissolution can be reduced.

  Next, the second invention will be described.

  Usually, coal is used as the carbon material supplied to the melting furnace. The bottom blowing is pulverized coal, and the charging from above is massive coal. Coal does not get wet with slag, and its specific gravity is smaller than that of slag. Therefore, the excess carbon material supplied into the furnace does not stay in the hot metal or slag, but is diffused into the furnace space. Carbon diffused in the furnace space causes a solution loss reaction, and the secondary combustion rate decreases.

  On the other hand, when a carbonaceous material is agglomerated in powder containing iron oxide and agglomerated and pre-reduced to produce reduced iron, if excessively added carbonaceous material, excess carbon is contained in the reduced iron. The Rukoto. When melting is performed using reduced iron containing excess carbon in this way, the specific gravity of reduced iron is greater than that of slag, so the carbon in the reduced iron dissolves in slag and hot metal without being scattered in the furnace space. It will be. Therefore, the secondary combustion rate can be improved and the secondary combustion rate can be kept good by using carbon in the reduced iron as a part of the supply source of the carbon material supplied to the melting furnace. The carbon input range can be expanded.

This invention is made | formed based on the said knowledge, In addition to the said 1st invention, the said reduced iron has a carbon content of 2-10 mass%, The ratio of the total carbon and total oxygen supplied to a melting furnace A method for producing molten iron, wherein (total carbon (kg) / total oxygen (Nm ³ )) is set to 0.9 to 1.5.
Total carbon (kg) = Carbon in supplied carbon (kg) + Carbon in supplied reduced iron (kg)
Total oxygen (Nm ³ ) = top blown oxygen amount (Nm ³ ) + FeO amount in reduced iron (kg) × 0.156 + Fe ₂ O _{3 in} reduced iron (kg) × 0.210 (2)

The first aspect of the present invention is a method for producing molten iron in which molten iron is obtained by supplying reduced iron together with carbonaceous material and oxygen to a melting furnace in which seed water is present. Even though the Al ₂ O ₃ and MgO concentrations in the slag are high, sufficiently good slag fluidity can be ensured, and as a result, the heat receiving efficiency is set to a high value, and the carbon materials and oxygen intensity required for melting Can be reduced.

  In the second aspect of the present invention, in addition to the first aspect of the present invention, by making the carbon content in the reduced iron 2% or more, the secondary combustion rate can be improved and the secondary combustion rate is good. The range of carbon input that can be maintained at a high level can be expanded.

  FIG. 1 shows a process flow showing an example of an embodiment of the present invention. In addition to a scrap melting furnace and a refining converter, it has a preliminary reduction furnace and a reduced iron melting furnace.

  Solid iron-containing cold material such as granule, mold, and steelworks generated scrap is supplied into the furnace of the scrap melting furnace 1 where the seed hot water is present. Coal is blown by using an oxidizing gas, for example, nitrogen gas as a carrier gas, thereby dissolving the supplied solid iron-containing cold material.

  The high carbon molten iron discharged from the scrap melting furnace 1 into the ladle is desulfurized together with the high carbon molten iron melted in the reduced iron melting furnace 9 in the desulfurization equipment 2 such as KR and injection. The high-carbon molten iron after desulfurization is charged into the refining converter 3 and supplied with oxygen for decarburization. For example, a general top-bottom blowing converter is used as the refining converter 3.

  As shown in the process flow of FIG. 1, dust generated in the scrap melting furnace 1 and the refining converter 3 (and the reduced iron melting furnace 9 described later) is transferred to the OG type wet dust collector 4 as shown in the process flow of FIG. After being dehydrated by the filter press 5 and further dehydrated by the filter press 5, lime as a binder and coal as a reducing material are additionally mixed and supplied to an agglomeration device 6, for example, a pan pelletizer, thereby being pelletized. At this time, when charging into a reduced iron melting furnace described later, the particle diameter is set to be 10 mm or more, for example, so as not to be lost due to scattering in the furnace rising gas flow. The production pellets are charged into the drying furnace 7. After drying, for example, a rotary hearth type prereduction furnace is used as the prereduction furnace 8, and heat reduction is performed using the internal coal as a reducing material in an air-LNG burner heating atmosphere to produce reduced iron.

For example, the dust composition: T.I. Fe = 62%, M.I. Using dust of Fe = 21%, FeO = 34%, Fe ₂ O ₃ = 22%, coal interior amount is 10%, binder (lime) amount: 10%, particle size: 10-15mm, moisture: 1% or less If reduced to 1200 to 1300 ° C. in a rotary hearth type prereduction furnace, reduced iron preliminarily reduced to a metalization rate of about 80 to 85% can be produced.

Dust generated and recovered in a scrap melting furnace or a refining converter contains about 2 to 3% of Al ₂ O ₃ . Moreover, about 3% of Al ₂ O ₃ is contained in the coal as the carbon material. Therefore, the reduced iron produced as described above contains about ₃ to 4% of Al ₂ O ₃ .

  In the present invention, the reduced iron produced as described above is supplied together with the carbonaceous material and oxygen to the reduced iron melting furnace 9 in which the seed hot water is present to produce high carbon molten iron. This reduced iron melting furnace 9 is hereinafter simply referred to as a melting furnace.

  The first invention will be described.

In the melting furnace, about 200 to 300 kg of slag is generated per 1 t of supplied reduced iron. Light calcined dolomite and light calcined magnesite are used as a secondary material for generating slag in addition to quick lime. By introducing these MgO sources and increasing the MgO concentration in the slag to 12 to 18%, the life of the MgO-C refractory, which is the refractory lining the melting furnace, is extended. As described above, since about ₃ to 4% of Al ₂ O ₃ is contained in the reduced iron, the Al ₂ O ₃ concentration in the slag is 12 to 12 together with the Al ₂ O ₃ in the carbonaceous material supplied at the same time. About 18%.

In the case where the slag contains high concentrations of MgO and Al ₂ O ₃ as described above, in order to keep the slag sufficiently fluid near the melting temperature of the melting furnace, what conditions should be used for the slag component? Conventionally, it has not been known whether it should be provided. Therefore, the relationship between the slag component, temperature, and slag viscosity was evaluated by measuring the viscosity of the actual slag.

The MgO and Al ₂ O ₃ concentrations in the slag are both fixed at 12 to 18%, and the slag basicity B (= CaO (mass%) / SiO ₂ (mass%)) is 1.59, 1.67, 1. The slag temperature was changed to 1380-1520 ° C., and the viscosity of the slag was measured. The plot in FIG. 2 shows the measurement results. It can be seen that the slag viscosity is expressed as a function of temperature and basicity B.

The viscosity is generally represented by the Arrhenius equation η = C · exp (E / RT). Here, T is an absolute temperature (K), C is a constant, E is an apparent activation energy, and both C and E are uniquely determined if the slag composition is determined. Here, if both MgO and Al ₂ O ₃ concentrations are fixed at 12 to 18%, C and E are functions of basicity B.

In general, as the basicity increases, the solid fraction of the slag increases, so the viscosity increases exponentially. Therefore, the slag composition dependence of the constants C and E often coincides with the actual viscosity when expressed by an exponential function of basicity B. Based on this concept, constants C and E were determined so as to match the actual viscosity shown in FIG. 2, and it was found that the viscosity (Pa · S) is represented by A in the following equation (1).
A = 7 * 10 < ^-7 > * exp (-6.2143 * B) * exp ((20663 * B + 7655.1) / T) (1)
However, B = CaO (mass%) / SiO ₂ (mass%), T: absolute temperature (K).

  The value A determined from the above equation (1) is shown by a solid line in FIG. It can be seen that it is in good agreement with the actual value plot.

Next, the reduced iron reduced by the preliminary reduction furnace was melted using a 100 t scale top-bottom blowing converter type melting furnace. The amount of seed hot water existing in the furnace is 50 tons, the amount of reduced iron to be charged is 40 tons, the amount of generated slag is 10 tons, the oxygen feed rate of top blowing oxygen is 7000 Nm ³ / h, and nitrogen gas is blown from the bottom blowing tuyere Coal powder was blown as a carrier gas. Blowing is performed so that (total carbon (kg) / total oxygen (Nm ³ )) is 1.1 when total carbon and total oxygen are settled by the above formula (2), and the secondary combustion rate is 25%. went.

Adjust the basicity in the slag and the molten iron temperature at the end of melting, change the value of A calculated by the above equation (1) from 0.3 to 6.3, and evaluate the relationship between the value of A and the heat receiving efficiency did. As a result, as shown in FIG. 3, when the value of A is 5 or more, it has been found that the heat receiving efficiency rapidly decreases. That is, by adjusting the basicity of the slag so that the value of A calculated by the formula (1) is less than 5 under the condition that both MgO and Al ₂ O ₃ concentrations in the slag are 12 to 18%. In addition, it is possible to secure the fluidity of the slag and to maintain the heat receiving efficiency from the furnace space to the molten iron at a high value.

  Therefore, if A is less than 5 and the fluidity of the slag is kept good, the distance between the top lance tip and the hot metal surface is properly maintained and the secondary combustion rate is kept high, the heat receiving efficiency is high. , Stable heat receiving is achieved.

  Moreover, if A is less than 5 and the fluidity of the slag is kept good, the covering effect of the molten iron surface by the slag is exhibited, and an improvement in yield due to a reduction in the amount of iron dust generated can be expected. Furthermore, stabilization of the secondary combustion rate can be expected by reducing the amount of carbon material scattered by bottom blowing. This is because the molten iron surface is not covered with slag with poor fluidity and the carbonaceous material is likely to be scattered, but in the case of slag with good fluidity, the molten iron surface is covered with slag, and it is considered that the scattering of the carbonaceous material is reduced.

In addition, the slag component range (mass%) is T.W. Fe: 0.1~3.0%, MnO: 0.1~4.0 %, MgO: 12~18%, Al 2 O 3: 12~18%, basicity: 1.2-2.0 of If it exists in the range, the said (1) Formula has validity, By making A of Formula (1) less than 5, the fluidity | liquidity of slag can be ensured favorable.

  The second invention will be described.

  Carbon steel and oxygen as a carbon source are supplied together with the iron-containing cold material to the melting furnace in which the seed hot water exists. Since the iron-containing cold material is dissolved by carburizing from the hot metal, the carbon content in the hot metal becomes insufficient as the iron-containing cold material is dissolved. Therefore, the supply of carbon materials supplements the deficient carbon in the hot metal. Moreover, the heat | fever required for melt | dissolution is supplied by combustion of carbon and oxygen. Furthermore, when the iron-containing cooling material is reduced iron containing unreduced iron oxide, carbon is consumed to reduce the iron oxide, and the heat of combustion of carbon and oxygen is required to compensate for heat loss during reduction. Therefore, the required carbon amount increases.

Since carbon and oxygen contained in the reduced iron are also supplied into the melting furnace, total carbon and total oxygen are defined by the following equation (2).
Total carbon (kg) = Carbon in supplied carbon (kg) + Carbon in supplied reduced iron (kg)
Total oxygen (Nm ³ ) = top blown oxygen amount (Nm ³ ) + FeO amount in reduced iron (kg) × 0.156 + Fe ₂ O _{3 in} reduced iron (kg) × 0.210 (2)
Here, the coefficients appearing on the right side of the total oxygen are 0.156 = 1 / 71.85 / 2 × 22.4, respectively.
0.210 = 48 / 159.7 / 32 × 22.4
Is a coefficient obtained as

  As described above, coal is usually used as the carbon material supplied to the melting furnace. The bottom blowing is pulverized coal, and the charging from above is massive coal. Coal does not get wet with slag, and its specific gravity is smaller than that of slag. Therefore, the excess carbon material supplied into the furnace does not stay in the hot metal or slag, but is diffused into the furnace space. Carbon diffused in the furnace space causes a solution loss reaction, and the secondary combustion rate decreases.

  When reduced iron containing unreduced iron oxide is used as the iron-containing cold material to be dissolved, as described above, the required carbon amount increases for reducing the iron oxide and for combusting to compensate for heat loss during reduction, The decrease in the secondary combustion rate due to the carbon diffused into the furnace space becomes more remarkable.

  By the way, when carbonaceous materials are agglomerated in powder containing iron oxide and agglomerated and pre-reduced to produce reduced iron, if excessively added carbonaceous materials, excess carbon is contained in the reduced iron. be able to. Thus, if it melt | dissolves using the reduced iron which contained carbon excessively, the carbon content contained in reduced iron can also function as carbon for a carbon concentration raise and combustion in hot metal. Furthermore, since the specific gravity of reduced iron is greater than that of slag, the carbon in the reduced iron does not scatter in the furnace space, but remains in the slag or hot metal, so it can be dissolved more efficiently than coal that has been conventionally used as a carbon material. Will be. Therefore, the secondary combustion rate can be improved and the secondary combustion rate can be kept good by using carbon in the reduced iron as a part of the supply source of the carbon material supplied to the melting furnace. The carbon input range can be expanded.

  Further, the reduced iron reduced in the preliminary reduction furnace is kept at a high temperature immediately after being extracted from the preliminary reduction furnace. If the high-temperature reduced iron is charged into the melting furnace without cooling, the amount of heat required for melting can be reduced. Furthermore, since the carbon contained in the reduced iron is also supplied to the melting furnace at a high temperature, the amount of heat required for melting is lower than that of carbonaceous materials supplied by bottom blowing or upward addition (these are supplied at room temperature). Furthermore, it has the effect that it can reduce.

FIG. 4 shows the metallization rate of the reduced iron when the carbon content in the reduced iron is changed from 1% to 15%, and the secondary when the reduced iron is used as the iron-containing cold material. The burning rate is shown. The metallization rate of reduced iron was about 60 to 80%, and the total carbon (kg) / total oxygen (Nm ³ ) based on the formula (2) was 1.2. All carbon was kept constant by adjusting the amount of bottom blown carbonaceous material. As is apparent from FIG. 4, the secondary combustion rate can be kept good by setting the carbon content in the reduced iron to 2% or more. More preferably, the carbon content in the reduced iron is 3% or more.

  In addition, when the carbon content in the reduced iron is too small, it means that the amount of the carbon material incorporated in the iron oxide before the preliminary reduction is small, and the reduction in the preliminary reduction furnace is insufficient and the metallization after the reduction. The rate will not be high enough. If the carbon content in the reduced iron is 2% or more, a metalization rate of 70% or more can be ensured, and it can be used without any problem as an iron-containing cold material as a melting raw material.

  Moreover, when there is too much carbon content in reduced iron, the intensity | strength of reduced iron will fall and it will become easy to pulverize at the time of handling or charging to a melting furnace. When reduced iron is pulverized, the carbon content in the reduced iron diffuses into the furnace space, causing a solution loss reaction, and the secondary combustion rate decreases. If the carbon content in the reduced iron is 10% or less, it can be used stably without causing the problem of powdering.

Next, a preferable range of the ratio of total carbon and total oxygen supplied to the melting furnace (total carbon (kg) / total oxygen (Nm ³ )) will be described.

If the amount of total carbon supplied is too much compared to total oxygen, excess carbon material will flow into the furnace space. The CO ₂ produced by the secondary combustion causes the following solution loss reaction with carbon floating in the furnace space and decomposes, resulting in a decrease in the secondary combustion rate.
C + CO ₂ → 2CO

  Moreover, since excess carbon is discharged out of the system as dust, sensible heat loss increases and productivity deteriorates.

The reduced iron reduced in the preliminary reduction furnace was dissolved using an upper bottom blown converter type vessel of 100 t scale. The metallization rate of reduced iron is 80%, and the carbon content in the reduced iron is 4%. The acid feed rate from the top blowing lance was 7000 Nm ³ / h, and coal powder was blown from the bottom blowing tuyere using nitrogen gas as a carrier gas. The value of total carbon / total oxygen was changed in the range of 0.8 to 1.7 kg / Nm ³ by changing the amount of blown coal, and the secondary combustion rate was evaluated. The results are shown in FIG. As can be seen from FIG. 5, if the total carbon / total oxygen value is 1.5 kg / Nm ³ or less, a secondary combustion rate of 25% can be secured, but the total carbon / total oxygen value is 1. It can be seen that the secondary combustion rate decreases when the amount exceeds 0.5 kg / Nm ³ .

  When the carbon content in the reduced iron is less than 2%, the upper limit of total carbon / total oxygen that can secure a secondary combustion rate of 25% decreases. This is because if the carbon content in the reduced iron is low, the proportion of the amount of blown coal increases, the amount of carbon material flying in the furnace space increases, and the secondary combustion rate tends to decrease.

Next, under the same conditions as in FIG. 5, the value of total carbon / total oxygen was changed in the range of 0.78 to 1.03 kg / Nm ³ , and the carbon concentration in the produced hot metal was evaluated. The molten iron temperature at the end of dissolution was also changed in the range of 1300 to 1450 ° C. The results are shown in FIG. As is apparent from FIG. 6, even with the same total carbon / total oxygen value, the lower the molten iron temperature, the lower the carbon concentration in the hot metal. If the range in which the molten iron temperature is 1300 ° C., which is the lower limit of normal operation, can ensure a carbon concentration in the molten iron of 4.0%, if the total carbon / total oxygen value is 0.9 kg / Nm ³ or more, then 4. It can be seen that a carbon concentration of 0% or more can be secured.

  Since the total carbon / total oxygen value is too low, the carbon concentration in the molten iron decreases to less than 4.0%, which may cause operational troubles such as bottom blown tuyere clogging, bullion attachment, and slopping. . If the bottom-blown tuyere is blocked, it will not be possible to supply charcoal, so it will be necessary to replace the tuyere and the operation will be stopped. If a bullion is attached to the furnace port, it will be difficult to extract and discharge, and the non-operation time will increase due to the removal of the bullion. If the top blow lance is attached with a bullion, it may cause trouble that the lance cannot be removed from the lance cone. When the carbon concentration in the molten iron decreases, the reduction rate of the iron oxide in the reduced iron decreases, and as a result, the T.I. Fe concentration rises and it becomes easy to slopp.

  Based on the above results, the value of total carbon / total oxygen in the present invention for dissolving reduced iron having a carbon content of 2% or more was defined as a range of 0.9 to 1.5.

  In the embodiment shown in FIG. 1 of the present invention, a reduced iron melting furnace 9 is prepared separately from the scrap melting furnace 1, and the reduced iron is melted in the reduced iron melting furnace 9. Since the scrap melting furnace 1 does not melt reduced iron, it is possible to prevent an increase in oxygen intensity and coal intensity due to iron oxide contained in the reduced iron, so that the molten iron productivity in the scrap melting furnace 1 can be reduced. It becomes possible to improve.

  Furthermore, the production of molten iron is shared by the scrap melting furnace 1 and the reduced iron melting furnace 9, and iron-containing cold materials other than reduced iron are melted in the scrap melting furnace 1, and the reduced iron is exclusively reduced in the reduced iron melting furnace 9. Since it melt | dissolves, the result of increasing the production capacity of molten iron can be obtained compared with the method of patent document 3 which melt | dissolves all the iron-containing cold materials containing reduced iron only by the scrap melting furnace 1. FIG.

  As the scrap melting furnace 1 and the refining converter 3, a converter having the same furnace capacity is generally used. In a converter plant having three converters of the same furnace capacity, when two of them are used as scrap melting furnaces 1 and the remaining one is used as a refining converter 3, two scrap melting furnaces 1 are The production capacity of the molten iron used is insufficient to cover the required amount of molten iron when a single refining converter 3 is fully produced. Therefore, in the method described in Patent Document 3, the refining-only converter 3 is forced to be manufactured in a state where the production capacity remains. In such a case, if the reduced iron melting furnace 9 is prepared as in the present invention and the melting of the reduced iron is left to the reduced iron melting furnace 9, the molten iron is produced only with two scrap melting furnaces. Thus, the total amount of molten iron produced can be increased. However, the refining converter 3 can be refined using all the produced molten iron as a raw material by using the production capacity. As a result, it becomes possible to increase the molten steel production capacity by more effectively utilizing the three converters in the converter factory having the existing three converters.

Dust recovered from the melting furnace and the refining furnace was reduced in a pre-reduction furnace to produce reduced iron having the component composition shown in Table 1. The carbon concentration in the reduced iron was 4.0% and the metallization rate was 80%. This reduced iron was melted in a melting furnace using a 100 t scale top-bottom blowing converter type vessel. The acid feed rate from the top blowing lance was 7000 Nm ³ / h, and coal powder was blown from the bottom blowing tuyere using nitrogen gas as a carrier gas. Further, quick lime for controlling the slag composition and light-burned magnesia were added into the furnace together with reduced iron from the upper hopper. Table 1 shows the composition of the auxiliary materials, and Table 2 shows the composition of the coal. Since the lining of the melting furnace is MgO-C brick, the MgO concentration in the slag was set to a range of 12 to 18% in order to protect the melting furnace refractory. Also, because it contains Al ₂ O ₃ in the reduced iron, slag concentration of Al ₂ O ₃ it became range 12 to 18%.

  The secondary combustion rate was adjusted to 25 to 26% by setting the total carbon / total oxygen value within an appropriate range of 0.9 to 1.5 and further setting the distance between the lance and the molten iron surface to 3.2 m. Under these conditions, the amount of secondary material input was adjusted to adjust the basicity B, and at the same time, the molten iron temperature was adjusted to change the value of A calculated by equation (1).

The secondary combustion rate is defined by the above-mentioned equation (3), but actually, the following equation (5) subtracting the influence of combustion due to the intruded air at the furnace port based on the analysis value of the flue gas Calculate by
Secondary combustion rate = [(CO ₂ %) i + (H ₂ O%) i-{(O ₂ %) a / (N ₂ %) a × 2 ・ ((N ₂ %) i-Q _N2 / Qi × 100)-2 ・ (O ₂ %) i} / [(CO ₂ %) i + (CO%) i + (H ₂ O%) i + (H ₂ %) i] × 100 (%) (5 )
Qi: Flue gas flow rate (Nm ³ / h)
Q _N2 : Amount of nitrogen gas blown into the furnace (Nm ³ / h)
(X%): Concentration of X component in furnace gas (vol%)
(X) a: Concentration of X component in air (vol%)
(X%) i: Concentration of X component in flue gas (vol%)

The flue gas was analyzed by gas chromatography for CO, CO ₂ , N ₂ , H ₂ and O ₂ , and H ₂ O by an absorption method (JIS Z8808).

  The iron dust generation intensity was calculated from the integrated value and production volume by measuring the iron dust concentration in the collected water.

  Heating efficiency is calculated by the above equation (4). In the calculation, various heats of reaction and sensible heat based on the mass balance were calculated, and the unknown heat quantity on the output side was obtained by taking the heat balance. Assuming that this unknown amount of heat is equal to the amount of heat (exhaust gas superheat) at which the exhaust gas is heated above the slag temperature, the calculation of equation (4) was performed. It is assumed that the molten iron temperature is equal to the slag temperature.

  The results are shown in Table 3. Of the slag components, the components other than those shown in Table 3 are expressed in mass% and T.I. The range was Fe: 0.1 to 3%, and MnO: 0.1 to 4%. Moreover, the amount of slag after melt | dissolution was 12-16 tons.

  Invention Example No. 1 in Table 3 1-7 are examples of the present invention. In all cases, the value of A was less than 5, and the fluidity of the slag could be ensured. As a result, a good result with a heat receiving efficiency of 90% or more could be obtained. The iron dust generation basic unit was small and good.

  On the other hand, Comparative Example No. In 8 to 11, the value of A was 5 or more and the fluidity of the slag was deteriorated, so that the heat receiving efficiency was less than 90%, and the iron dust generation unit was increased.

  The same furnace as in Example 1 was used, and reduced iron was dissolved under the same conditions except as otherwise specified below.

By keeping the acid feed rate constant, the total oxygen was kept constant at 5000 Nm ^3, and the feed rate of bottom-blown pulverized coal was changed to vary the total carbon, thereby varying the total carbon / total oxygen value. . The target secondary combustion rate was 25%. The distance between the tip of the lance and the molten iron surface was 3.2 m except for a part.

  No. shown in Table 4 About 12-30, all set the value of A of Formula (1) to less than 5, and slag fluidity was kept favorable. On the other hand, the “No. 1 + 2” No. Nos. 12 to 21 are within the scope of the first and second inventions, whereas “No. 1” indicating “present invention 1”. About 22-30, although it exists in the 1st invention range, it is the conditions remove | deviated from the range of the 2nd invention.

No. About 12-21, since the carbon content in reduced iron is 4.0% and the value of total carbon / total oxygen is also in the favorable range of 0.9-1.5 kg / Nm ³ , the secondary combustion rate The heat receiving efficiency was good, and the carbon concentration in the molten iron after melting was a good value of 4.0% or more.

  No. Regarding Nos. 22 and 23, the total carbon / total oxygen value was too low and the total carbon supply amount was insufficient, so the carbon concentration in the molten iron after melting was less than 4.0%. No. For 24-26, the value of total carbon / total oxygen was too high, and the surplus carbon content floated in the furnace space, resulting in a decrease in the secondary combustion rate. No. For 27 and 28, the total carbon / total oxygen value is high, so the lance height is set higher than the appropriate value for the purpose of improving the secondary combustion rate. Results in a decline.

  No. For No. 29, the carbon concentration in the reduced iron was too high, pulverization of the reduced iron occurred, and the pulverized carbon in the reduced iron floated in the furnace space, resulting in a decrease in the secondary combustion rate. . No. About 30, since the carbon concentration in reduced iron is low, it is the level which the supply amount of pulverized coal increased in order to ensure all carbon. Since pulverized coal tends to float in the furnace space, the secondary combustion rate decreased.

It is a figure which shows an example of the process flow of this invention. It is a figure which shows the relationship between slag temperature, slag basicity, and a viscosity. It is a figure which shows the relationship between the value of A of (1) Formula, and a heat receiving efficiency. It is a figure which shows the relationship between the carbon concentration in reduced iron and a secondary combustion rate, and the relationship between the carbon concentration in reduced iron and the metallization rate of reduced iron. It is a figure which shows the relationship between the value of total carbon / total oxygen, and a secondary combustion rate. It is a figure which shows the relationship between the value of total carbon / total oxygen, and the carbon concentration in molten iron. It is a figure which shows an example of the conventional process flow.

Explanation of symbols

1 Scrap melting furnace (converter for melting only)
2 Desulfurization facility 3 Converter for refining 4 Wet dust collector 5 Filter press 6 Agglomeration device 7 Drying furnace 8 Prereduction furnace 9 Reduced iron melting furnace

Claims (1)

A powder containing iron oxide is agglomerated with a carbonaceous material, agglomerated, preheated at a high temperature in a prereduction furnace and preliminarily reduced using the carbonaceous material as a reducing material, and the produced reduced iron is seeded together with the carbonaceous material and oxygen. is supplied to the melting furnace in the presence of water, by mass% slag composition to produce on the molten _{iron, Al 2 O 3: 12~18%} , MgO: with a 12 to 18%, of the produced slag basicity B And A in the following formula (1) relating to the molten iron temperature T (K) after melting is less than 5 , the reduced iron has a carbon content of 2 to 10% by mass, and includes all the carbon and all oxygen supplied to the melting furnace. A method for producing molten iron, wherein the ratio (total carbon (kg) / total oxygen (Nm ³ )) is 0.9 to 1.5 .
A = 7 * 10 < ^-7 > * exp (-6.2143 * B) * exp ((20663 * B + 7655.1) / T) (1)
B = CaO (mass%) / SiO ₂ (mass%)
Total carbon (kg) = Carbon in supplied carbon (kg) + Carbon in supplied reduced iron (kg)
Total oxygen (Nm ³ ) = top blown oxygen amount (Nm ³ ) + FeO amount in reduced iron (kg) × 0.156 + Fe ₂ O _{3 in} reduced iron (kg) × 0.210

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